1. Field of the Invention
The present invention relates to an optical coupling module which realizes a coupling between a two-dimensional surface emitting laser array and a two-dimensional optical fiber array, and to a method of producing the same.
2. Description of the Related Art
With a growing interest in optical interconnection, much effort is being made toward the development of parallel optical transmission using a semiconductor laser array (hereinafter, also referred to simply as "a laser array"). In particular, a parallel optical transmission using a surface emitting semiconductor laser (hereinafter, also referred to simply as "a surface emitting laser") as a light source is receiving much attention, and research and development in this area are being conducted vigorously. The reason is that the surface emitting laser, for example, a vertical cavity type surface emitting laser, has characteristics suited for the light source for parallel optical transmissions. For example, it can be integrated into a high density two-dimensional laser array. The characteristics also include low power consumption and low production cost. Moreover, since the emitted beam is circular in shape, it can readily be combined with optical fibers.
A conventional optical coupling module which can be used for the parallel optical transmission is typically constituted of a one dimensional semiconductor laser array and a one dimensional optical fiber array combined together as disclosed, for example, in Japanese Laid-Open Patent Publication No. 6-34853. FIG. 13 illustrates the structure of the conventional optical coupling module 1300 disclosed in the above-mentioned publication.
The conventional optical coupling module 1300 has a one dimensional semiconductor laser array 1302 and a plurality of parallel V grooves 1303, both formed on a silicon substrate 1301. The V grooves 1303 are aligned such that the location of each V groove corresponds to one of the laser devices included in the semiconductor laser array 1302. The semiconductor laser array 1302 may be formed separately and installed later on the silicon substrate 1301. Each optical fiber wire 1305 included in a multi-wire optical fiber tape 1304 is disposed in each of the V grooves 1303 and secured with an adhesive agent. This realizes optical coupling between the laser devices included in the semiconductor laser array 1302 and the optical fiber wires 1305 included in the optical fiber tape 1304.
However, when a two-dimensional surface emitting semiconductor laser array is involved, the above-described conventional structure cannot realize optical coupling between all laser devices included in the laser array and optical fiber wires included in the optical fiber tape. Moreover, in order to arrange the optical fiber tape in such a manner that the tape is parallel with the substrate while mounting both the optical fiber tape and the two-dimensional surface emitting semiconductor laser array on the same substrate, it is necessary to mount the laser array on the substrate such that it is perpendicular to the substrate. Such mounting, however, is practically difficult.
Furthermore, a plurality of silicon substrates having the V grooves of the above-described conventional structure can be stacked with one on the top of another for multiple layers and vertically placed in contact with the two-dimensional surface emitting semiconductor laser array mounted on another substrate in an attempt to achieve optical coupling between laser devices included in the laser array and optical fiber wires. However, since the V grooves formed on each substrate become easily misaligned in the horizontal direction upon stacking, it is difficult to accurately match each optical fiber wire included in the optical fiber tape to the corresponding laser device included in the two-dimensional surface emitting laser array.
On the other hand, Japanese Laid-Open Patent Publication No. 6-237016, which corresponds to U.S. Pat. No. 5,434,939, proposes a module which has a structure including guiding holes formed in the substrate having a two-dimensional surface emitting laser array formed thereon, the location of the guiding hole corresponding to one of the laser devices included in the laser array. The optical fibers are then inserted in the guiding holes for optical coupling with the laser device. However, this structure cannot ensure sufficiently strong coupling strength since the optical fibers are simply inserted into the guiding holes. Moreover, in a case where the number of laser devices included in the laser array is large, the number of optical fibers to be coupled is also large, which means that the number of couplings increases and the efficient attainment of optical coupling becomes difficult.